[Mithadan]

Could be.

Like you, I tend to try to resolve all questions regarding Tolkien's published writings in favor of consistency. Your theory would potentially resolve the inconsistency. Of course. there are others here who might simply say "he made a mistake."

There's a thread below, "Seriously - what was it that scared Gandalf to look more into Bilbo's ring?" that also addresses inconsistencies in LoTR, with the same two viewpoints taken.